Antireflection coatings are used to suppress or reduce optical reflections on optical surfaces, such as lenses, objectives, prisms, plates, and the like, and to increase the transmittance. A reduction in the degree of reflection on the coated surface may be achieved by a destructive interference of the reflected beams. For this purpose, an antireflection layer is applied to the described optical surfaces.
An alternative approach for reducing reflections on optical surfaces is nanostructures on the object surface. Geometric dimensions and distances between such structures must be smaller in this case than the wavelength of the incident optical radiation. Geometric shapes that effectuate an essentially continuously varying refractive index, such as acute-angled frustums, are suitable nanostructures. A smooth transition of the refractive index reduces the degree of reflection without great wavelength and angle dependency. With optimized structure geometries, a reflex reduction which is independent from the polarization is also possible. An antireflection effect due to nanostructures formed on the surface is referred to as the so-called “moth eye effect.”
German Patent Application No. DE 10 2007 014 538 A1 describes a method which allows moth eye structures to be generated directly on fused silica with the aid of etching.